Microwave beam transmitter



7', 1958 w. 0. WHITE MICROWAVE BEAM TRANSMITTER Filed April 30, 1953Inventor: William C.Whit,e,

by His Attorney.

MICROWAVE BEAM TRANSMITTER William C. White, Schenectady, N. Y.,assignor to General Electric Company, a corporation of New YorkApplication April 30, 1953, Serial No. 352,085 51Claims. (Cl. 315-34 Myinvention relates to microwave beam transmitters. Beamed sources ofmicrowave energy are finding increasing numbers of applications,especially in industry where they may be employed in detection andcontrol systems. In such applications, however, the use of laboratorytype of equipment is becoming increasingly inconvenient and impracticalsince such equipment requires special skills in operation andmaintenance. It is further desirable that this type of apparatus, whichincludes discharge devices, resonators, and antennas, be incorporated inunitary assemblies which are compact and sturdy and meet the usualrequirements of low cost and trouble-free construction.

It is therefore a primary'object of my invention to provide an improvedand simplified microwave beam transmitter construction.

It is another object of my invention to provide a microwave beamtransmitter suitable for industrial applications. i

In accordance with my invention the electrodes of a discharge device, anoscillator resonator system, and

an antenna are positioned within a parabolic reflector,

the face plate for the reflector being sealed thereto to complete thevacuum chamber for all the components of a microwave beam transmitterincluding the discharge device electrodes. Since the components are allwithin one vacuum enclosure, no insulating seals for themicrowave-energy conductors are required, the only seals being those forthe discharge device cathode and for the anode leads.' In a preferredembodiment the electrode leads-also serve to support the oscillatorassembly and to thus position the antenna near the focus of theparabolic reflector. Only direct current and heater current connectionsneed be made to the terminals of the unitary assembly thus provided sothat a minimum of training and skill is required for the operation andmaintenance of the transmitter;

' The novel features which I believe to be characteristic of myinvention are set forth with particularity in the appended claims. Theinvention itself, however, both as to its organization and method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconnection with the accompanying drawing in which the single figure is aview, partly in section, of a microwave transmitter embodying myinvention.

Referring now to the drawing a microwave beam transmitter is positionedwithin a parabolic reflector 1 suitably made of a glass bowl having aparabolic curve with an inner metalized coating 2 to provide areflecting surface forelectromagnetic waves. A glass face plate 3 sealedto the rim of the bowl encloses the reflector and provides a vacuumenvelope for an oscillator 4 and antenna 5 contained therein. Acylindrical glass neck 6 .is fused between the base and the reflectorbowl 1 to facilitateclamping it to a mechanical support 7. In order thatthe transmitter may be either held or stationed as desired, the supportmember 7 suitably includes metal straps 8 which are tightened around thecylindrical base' portion 6 and fastened together by a bolt 9 so thatthe clamp can be readily loosened to permit the removal of thetransmitter and insertion of a replacement unit.

Within the reflector bowl the oscillator 4 includes a triode dischargedevice designed for operation in a high vacuum and having respectively acathode 10, a control grid electrode 11-and an anode 12, the operatingsurfaces of these electrodes being disk-shaped and arranged in parallelplanes. Each electrode is provided with suitable cylindrical conductiveterminals and insulating spacers are positioned between the electrodesto hold them in the desired relationship.

In the particular discharge device construction illustrated in thedrawing the cathode 10 is made in the form of a cylinder or eyelethaving a closed end constituting the active cathode surface and having aflange at the other end. One end of an internal heater element shaped todefine an annular recess or grid-anode cavity resonator between it andthe grid washer 11. The portion of the anode flange 17 adjacent the gridwasher is spaced therefrom by an insulating washer 18, suitably made ofa ceramic material. The anode is apertured to facilitate evacuation ofthe interelectrode spaces.

To complete the oscillator assembly an annular flanged metallicresonator member 19 is provided, the outer flange being slipped over theperiphery of the anode flange 17 and the inner flange being positionedaround the flange of the cathode 10. An insulating spacer, suitablyprovided by a band of a ceramic or mica 20, is positioned between themember 19 and the cathode between them. The grid-cathode cavityresonator is thus defined by the resonator member 19, the cathode 10 andthe grid 11, the grid-cathode spacer 15 being a dielectric and hence initself comprising part of the resonator. In a vacuum tube, theinsulating ceramic spacing disks must be continuous and vacuum tight butfor the assembly described here, Where the whole enclosure is evacuated,this is not necessary and spoked-wheel design of spacer disks'can beemployed. Thus lowered dielectric losses are obtainable as less ceramicmaterial is in the highfrequency electric fields. When the cathode isheated to emit electrons and a positive voltage is applied to the anodethe oscillator will operate at the frequency established by theresonators.

In this case, the grid-anode resonator, being the physically smaller ofthe two, establishes the operating frequency and the space enclosed bythe grid-cathode resonator is adjusted by sliding the annular resonatormember 19 over the anode flange so that a harmonic of the grid-cathoderesonator frequency corresponds to either the fundamental or a harmonicfrequency of the grid-anode resonator. Coupling between the tworesonators is provided by both the interelectrode capacitances and alsoby the path between the resonators through the spacing insulator 17. Inthe particular resonator construction shown the operating frequency isdesigned to be of the order of 5000 megacycles, the Wave length at thisfrequency beingsufliciently small so that a reflector of relativelysmall dimensions, such as suitable for portable use, will operateefiectively to beam the high frequency energy.

Energy from theresonator is suitably coupled to the antenna 5 positionednear the focus of the parabolic wave of the reflector 1. A dipoleantenna is conveniently made from a length of copper wire havingoppositely extending quarter wavelength end portions and parallel centerportions with the center loop 22 extending into the grid-cathoderesonator for coupling to the high frequency energy thereof. An aperturein a portion of the resonator facing the base of the reflector holds aninsulating grommet 23 having parallel bores through which the wire endscomprising the antenna are inserted before the end portions are bentover. A shield 24 comprising a metallic disk is fixed on the antennagrommet to prevent direct outward radiation from the antenna, the energyradiated being directed towards the parabolically curved walls of thereflector. As is well known in the parabolic reflectors, the energyemanating from the focal point thereof or a point nearby is reflectedalong paths substantially parallel to the parabolic axis, thusconcentrating the reflected energy in a beam. Since the dimensions ofthe parabola are not large with respect to the Wavelength of thereflected energy, the parabola should be designed so that the distancefrom the focus to the reflector is one-fourth wavelength or on oddmultiple thereof at the desired frequency.

The entire resonator and antenna assembly is preferably supported withrespect to the reflector 1 by the electrode leads required forapplication of direct current and heater potentials to the dischargedevice elements. As shown in the drawing three conductive rods orelectrode leads positioned parallel to the parabolic axis are employed,lead 25 being welded to the anode, lead 26 to the cathode flange, andlead 27 to the heater terminal. The leads extend through the bottom ofthe reflector 1 and the neck 6, the exposed outerends of the leadsserving as base pins which are engaged by a socket 28 connected by acable 29 to the heater and anode voltage sources represented asbatteries 30 and 31 respectively. As will be noted, no high frequencyleads need be sealed through the reflector, thus eleminating sealproblems usually occurring where high frequency insulating seals arerequired.

By virtue of the unitary assembly thus provided, with the oscillator andantenna enclosed in the common vacuum envelope defined by the parabolicreflector, the transmitter is adapted for installations and hand-heldoperation with a minimum of skill required for operation andreplacement. Any adjustments are made before the face-plate 3 is sealedand the reflector evacuated, thus removing any possibility of tamperingwith the transmitter.

The whole assembly may be evacuated by heating the glass envelope in anoven and later heating the electrodes by bombardment or high-frequencyinduction heating while the envelope is being pumped through thetubulation 32, after which the envelope is sealed off from the system at33. These procedures are well known in connection with the manufactureof vacuum tubes. While a particular type of discharge device has beendescribed in connection with the illustrated embodiment of my invention,it will be understood, of course, other discharge device types may besubstituted.

While the present invention has been described by reference to aparticular embodiment thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the invention. I, therefore, aim in the appended claimsto cover all such equivalent variations as come within the true spiritand scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A microwave discharge device beam transmitter having an hermeticenvelope, said envelope comprising a parabolic electromagnetic reflectorand a dielectric face-plate sealed thereto, an oscillator structurepositioned therein having electron discharge device cathode, grid, andanode electrodes, means for applying voltages to said electrodes, saidmeans for applying said voltages being insulatingly sealed through saidenvelope, and an antenna coupled to said oscillator positioned near theparabolic focus of said reflector.

2. A microwave discharge device beam transmitter having an hermeticenvelope, said envelope comprising a parabolic electromagnetic reflectorand a dielectric face-plate sealed thereto, an oscillator structurepositioned therein having electron discharge device cathode, grid, andanode electrodes, means for supporting said oscillator structure and forapplying voltages to said electrodes comprising stiff conductive membersinsulatingly sealed through said envelope, and an antenna coupled to sad oscillator positioned near the parabolic focus of said reflector.

3. An ultra-high frequency beam transmitter comprising a parabolicelectromagnetic reflector, discharge device electrodes including acathode, a grid, and an anode positioned within the region described bysaid reflector, a first resonator coupled to said cathode and said grid,a second resonator coupled to said grid and said anode, feed-backcoupling conducting means between said resonators, means for applyingexternal potentials to said electrodes, said conducting means beinginsulatingly sealed through said reflector near the center thereof, anantenna coupled to one of said resonators, said antenna being positionednear the focal point of said reflector, and a gas impervious insulatingface-plate hermetically secured to said reflector to enclose saiddischarge device, electrodes, resonators, and antenna and complete avacuum envelope therefor.

4. An ultra high frequency apparatus comprising a parabolicelectromagnetic reflector, electron discharge device electrodespositioned within the region described by said reflector including aplanar cathode, a grid, and an anode, a first resonator coupled to saidcathode and said grid, a second resonator coupled to said grid and saidanode, feed-back coupling means between said resonators, conductingmeans for applying external potentials to said electrodes, saidconducting means being insulatingly sealed through said reflector, anantenna coupled to one of said resonators, said antenna being positionednear the focal point of said reflector, and a gas impervious insulatingface plate hermetically secured to said reflector to enclose saiddischarge device electrodes, resonators, and antenna to complete avacuum envelope therefor.

5. A microwave beam transmitter comprising a parabolic electromagneticreflector, electron discharge device electrodes positioned within theregion described by said reflector including a planar cathode, a grid,and an anode, conducting means for supporting said device and forapplying external potentials to said electrodes, said conducting meansbeing insulatingly sealed through said reflector, a resonator systemcomprising a grid-cathode resonator and a grid-anode resonator withfeed-back coupling means therebetween coupled to said respectiveelectrodes, an antenna coupled to one of said resonators positioned nearthe focal point of said reflector, and a glass face plate hermeticallysecured to the reflector rim to enclose said discharge deviceelectrodes, said resonator system, and said antenna to define a vacuumenvelope therefor.

References Cited in the file of this patent UNITED STATES PATENTS1,958,591 Roberts May 15, 1934 52,339 Dallenbach Aug, 25, 1936 2,404,261Whinnery July 16, 1946 35,804 Spooner Feb. 10, 1948 76,725 GurewitschJuly 19, 1949 76,971 Fremlin et a1 July 26, 1949 0,603 Dorgelo Nov. 21,1950

